Vapor generator

ABSTRACT

A vapor generator for a Rankine cycle engine includes an elongated heat exchange tube for conducting engine working fluid therethrough. A temperature-responsive mechanism extends along the heat exchange tube for sensing the average temperature along its length and also the temperature at any segment of its length. The temperature-responsive mechanism produces a signal from which operation of the vapor generator heat source is influenced as function of either one or both of these temperature conditions.

0 United States Patent 1 1 3,734,402

Morgan [4 1 May 22, 1973 [541 VAPOR GENERATOR 3,511,970 5 1970 Kjellberg..236/99 x 3,205,871 9/1965 Higgins et a1... ..122/504 [75] Invent DeanMorgan Sudbury Mass 2,565,350 8/1951 Burns et a1. ..236/78 B x [73]Assignee: Thermo Electron Corporation,

Waltham, Mass. Primary ExaminerWilliam E. Wayner [22] Filed: Oct. 18,1971 Attorney-James L. Neal [21] Appl. No.: 189,949 57 B TRA T A vaporgenerator for a Rankine cycle engine includes 1.8. CI. B, an elongatedheat exchange tube for conducting en- 122/504, 236/99 gine working fluidtherethrough. A temperature- [51] Int. Cl. ..F22b 37/47 responsivemechanism extends along the heat [58] Field of Search ..236/2l B, 21 R,32, exchange tube f sensing the average temperature 236/178 95; 122/504;73/340 349, along its length and also the temperature at any seg- 368ment of its length. The temperature-responsive mechanism produces asignal from which operation of [56] References cued the vapor generatorheat source is influenced as func- UNITED STATES PATENTS tion of eitherone or both of these temperature condiions. 2,016,317 10/1935 Dahl..236/32 2,822,985 2/ 1958 Johnson et a1 ..236/99 11 Claims, 8 DrawingFigures Patented May 22, 1973 3,734AG2 Z5 Sheets-Sheet 1 -12F -2Patented May 22, 1973 3 Shoots-Sheet 1.1

K164 BURNER CUT-OFF FUEL-AIR CONTROL auauen cur oown 36 242 15g r f f MCONTROL I CONTROL BURNER 5 m Mews BOILER EXPANDER 1 o 'REGEN- 146 Fig 2ERATOR PUMP couoaussn VAPOR GENERATOR BACKGROUND OF THE INVENTIONRankine cycle engines are experiencing an increase in importance as aresult of both technological advances and their relativelypollution-free operation. One area of technological advance involvesorganic working fluids and vapor generators complimentary to theseworking fluids. In Rankine cycle systems, efficiency is enhanced byoperation at relatively high vapor generator outlet temperatures.Organic working fluids, however, tend to be characterized by maximumtemperatures beyond which they will begin to rapidly deteriorate. Someworking fluids which are otherwise suitable for use in Rankine cyclesystems, when overheated, will not only deteriorate, but will alsoproduce substances which attack certain components of the vapor enginesystem. Thus, overheating of the working fluid may, in addition tosharply reducing the performance levels of the system, produce permanentdamage to the system components.

SUMMARY OF THE INVENTION This invention pertains to a vapor generatorfor Rankine cycle or vapor engines in which working fluid to bevaporized is circulated through an elongated heat exchange tube. Workingfluid in the tube is subject to overheating in at least two ways. First,a relatively large portion of the heat exchange tubing in the vaporgenerator may become substantially uniformly overheated. Second,overheating may occur along a relatively short segmental portion of theheat exchange tube.

To monitor the temperature of the heat exchange tube, there is providedsensing apparatus which extends therealong lengthwise. The sensingapparatus includes sealed sensing tube means in good thermalcommunication with the heat exchange tube and containing sensing liquidadapted to vaporize substantially at the maximum temperature to whichthe working fluid can be heated without deterioration.

Fluid within the sensing tube expands and contracts according to theaverage temperature change within the heat exchange tube and thusproduces a first signal functionally related to such average temperaturechange. This signal may be used to influence the heat source for thevapor generator to, for example, maintain the system below a presettemperature. Since the sensing fluid within the sensing tube means willvaporize at the maximum temperature which the working fluid canwithstand, an abrupt relatively large volumetric expansion of thesensing fluid will be experienced when the maximum temperature isreached in any segmental portion of the heat exchange tube. This abruptvolumetric change of the sensing fluid produces a second signal whichindicates a hot spot along some portion of the heat exchange tube. Thisis usually indicative of some abnormality in the operation of thesystem. Accordingly, the second signal is appropriately used to overrideother signals and, for example, cut off the vapor generator heat source.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view ofone embodiment of this invention;

FIG. 2 is a cross-sectional view of FIG. 1 taken along line 2-2;

FIG. 3 illustrates an alternate embodiment of the invention;

FIG. 4 illustrates another embodiment of the invention;

FIG. 5 is a cut-away view illustrating one embodiment of a controlmechanism usable with the apparatus of FIG. 4;

FIGS. 6a and 6b are cross-sectional views of FIG. 5 showing theapparatus in various positions; and

FIG. 7 is a schematic diagram of a Rankine cycle engine incorporatingthe present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Reference will now be made to FIGS.1 and 2. A vapor engine boiler 10 includes a heat exchange means 12 anda control means 14. A housing 16 for the heat exchange means 12 formsopposed headers. There is shown in FIG. 2 a group of headers designated18, 20, 22 and 24. Extending between the opposed headers, for conductingworking fluid 33 through the heat exchange means 12, are heat exchangetubes which include a set 26 of relatively large tubes 30 and a set 28of relatively small tubes 32. The tubes 32 have associated therewith aplurality of generally parallel thermally conductive fins 34 situatedperpendicularly of the tubes. Spaced from the heat exchange tubes 30 isburner means 36, the intervening space between the burner means and theheat exchange tubes 30 constituting a combustion chamber 37.

Associated with the heat exchange means 12 is the control means 14including a pair of heat sensing tube means 39 and 41 which include,respectively, relatively small sensing tubes 38 and 40 extending alongthe heat exchange tubes 30 and to the housing means 50 for fluidcommunication with the bellows 42 and 44. The sensing tube means 39 and41 are filled with sensing fluids 56 and 64. Simplicity of operationwill, in most circumstances, suggest that sensing fluids 56 and 64 beidentically the same, though this identity is not essential. The sensingtubes 38 and 40 are mall relative to the heat exchange tubes with whichthey are associated and may be attached to the associated heat exchangetubes in any convenient manner which produces good thermal conductivity.This conductivity may be accomplished by brazing the sensing tubes 38and 40 to the heat exchange tubes 30 and/or 32, with the sensing tubesbeing either inside or outside of the heat exchange tubes. While thesensing tubes 38 and 40 are shown as extending along all the heatexchange tubes 30, it should be understood that they may extend alongonly a portion of those heat exchange tubes or they may be configured toextend along any or all of the relatively small heat exchange tubes 32.

Extending from the bellows 42 is a supporting arm 45 upon which ismounted a microswitch 46 having an actuating member 48. The bellows 42rests upon the housing means 50. There also extends from the housingmeans 50 a spring confining member 52 which is bifuricated to extendpast the supporting arm 44. Interposed between the member 52 and thebellows 42 is a spring means 54 which applies a predetermined pressureto the sensing fluid 56 in the bellows 42 and the sensing tube 38.Projecting from the bellows 44 is a switch actuating arm 58 which isengageable with the actuator 48 of the microswitch 46. From the housing50, a second spring confining member 60 extends past the arm 5 8.Between the spring supporting member 60 and the bellows 44 is a springmeans 62 which applies a predetermined pressure to the sensing fluid 64within the bellows 44 and the sensing tube 40. The pressure applied tothe sensing fluid 64 in the sensing means 41 is such that the vaporpressure of the sensing fluid 64 will equal the externally appliedsensing fluid pressure substantially at the maximum permissabletemperature for the working fluid 33 in the heat exchange tubes. Inother words, the sensing fluid 64 will vaporize at the maximumpermissable working fluid temperature, where the vapor pressure of thesensing fluid equals the externally applied pressure in the sensingfluid. The spring means 54 applies to the sensing fluid 56 in thesensing means 39 sufficient pressure to cause the vapor pressure of thesensing fluid 56 to equal the pressure in the fluid only at atemperature above the maximum permissable temperature for the workingfluid 33 and, preferably, only at a temperature above the maximum systemtemperature which can be anticipated. Consequently, the sensing fluid 56will vaporize only at a temperature above the maximum permissabletemperature for the working fluid 33 and, preferably, will not vaporizeat all.

The sensing tube means 39 serves as a thermal expansion monitor for thesensing tube means 41 so that sensitivity of the sensing tube means 41to the maximum permissable working fluid temperature is not lost.Without the sensing tube means 41, the sensitivity of the sensing tubemeans 39 to the maximum permissable working fluid temperature woulddecrease as a function of the length of the sensing tube 40. This occursbecause, with relatively long sensing tubes, the thermal expansion andcontraction of the sensing fluid attending an overall temperature changewithin the system will be of such a magnitude that it will become verydifficult, if not impossible, to distinguish between sensing fluidvolume changes occurring because of such thermal expansion and volumechange occurring because of vaporization of sensing fluid at arelatively small segmental length of the sensing tube.

Numerous fluids having a critical temperature above the anticipatedmaximum system temperature are usable as sensing fluids, the fluidproperties being selected as appropriate for each particular system.Examples of suitable sensing fluids are Dowtherm A manufactured by DowChemical Company of Midland, Mich; Freon E-3, Freon E-4 and Freon E-5manufactured of by E. I. du Pont de Nemours & Co., Inc. of Wilmington,Del., and pyridine.

Operation of the apparatus illustrated in FIGS. 1 and 2 will now bedescribed.

The boiler accepts the working fluid 33 through an inlet 66. The workingfluid 33 circulates successively through the heat exchange tubes 30 andthen through the heat exchange tubes 32 from whence it passes from theboiler through an outlet, not shown. The burner means 36 sustainscombustion of a fuel-air mixture in the combustion chamber 37. Productsof combustion pass between the heat exchange tubes 30 and 32 and outthrough an exhaust passage, not shown, and heats the working fluid inthe heat exchange tubes. The temperature of the working fluid must notbe permitted to exceed the temperature above which the particularworking fluid will begin to deteriorate. Accordingly, the control means14 provides a signal which may be used to control operations of theburner means 36. One example of such control will be subsequentlydescribed in connection with FIG. 7.

The hot products of combustion from the burner means 36 passing throughand around the heat exchange tubes 30 heat both the heat exchange tubesand the sensing tubes 38 and 30. The heat exchange tubes and the sensingtubes have substantially identical temperature profiles. That is, at anylocation, adjacent segments of tubes will be at the same temperature.When the sensing fluids 56 and 64 within the sensing tube means 39 and41, respectively, are heated, they both expand in substantiallyidentical amounts as long as temperatures are below the predeterminedmaximum temperature for the working fluid 33. As the temperaturechanges, the volumetric changes of the fluid within the sensing tubemeans 39 and 41 are equal. An increase or decrease in temperaturethereby causes a corresponding movement of both the supporting arm 44and the switch actuating means 58, as indicated by arrows 68 and 70, butno relative movement between the microswitch 46 and the actuator arm 58is produced. The microswitch 46 does not sense the temperature change.However, movement of the supporting arm 44 with its associatedmicroswitch 46 and/or the switch actuating arm 58 may provide a signalas a function of boiler temperature change by actuating the microswitch59. The actuation of the microswitch 59 may be used to cause a lowerstage of combustion in zone 38.

If certain abnormal conditions develop within the boiler 10, hot spotsmay develop along one or more relatively small linear segments of theheat exchange tube 30. For example, if due to some malfunction of theburner means 36, a large portion of the products of combustion aredirected to a relatively small portion of the heat exchange tubes withinthe boiler, there will develop at this point an excess of heat energycapable of overheating the working fluid 33. In this event, the sensingfluids 56 and 64 within the sensing tubes 38 and 40, respectively, willexpand by equal volumetric amounts until the predetermined maximumtemperature for the working fluid 33 is reached. When this predeterminedtemperature is reached at any segmental length of the heat exchange tube30, the sensing fluid 64 in the adjacent segment of the sensing tube 40will vaporize. The fluid volume within the sensing tube menas 41 willthereby experience a sudden volumetric expansion as compared to theexpansion which will take place within the sensing tube means 39. Theexpansion of the sensing fluid within the sensing tube means 41 willcause the switch actuating arm to move outwardly from the bellows 44,against the bias of the spring 62 and actuate the microswitch 46. Thesignal from the microswitch 46 may be used to influence the operation ofthe burner means 36 so as to reduce or en tirely cut off the heat inputinto the boiler and thereby avoid overheating of the working fluid 33.

A boiler of smaller heat producing capacity is illustrated in FIG. 3wherein like numerals are used to designate like parts. The apparatusconsists of heat exchange means 12 and a control means 14. The heatexchange means includes an insulated tubular wall member forming achamber within which a heat exchange tube 72 is wound in spiral fashion.Within an interior space formed by the spirally wound heat exchange tube72 is a burner unit 74 and a baffle structure 76. The burner 74 includesan inlet 76 which admits an air and fuel mixture thereto. The mixturepasses through a porous wall 78 of the burner 74 where combustion takesplace. The products of combustion pass across a portion of the tube 72,through the baffle 76, onto the remainder of the tube 72 and out throughan exhaust opening 80. Working fluid 33 enters the boiler through aninlet 82 of the heat exchange tube 72 and circulates through the tube 72where it is vaporized. The vapor passes from the tube 72 through anoutlet 84 The control means 14 operates in the same manner as whenassociated with the apparatus described in connection with FIGS. 1 and2. A pair of sensing tube means 39 and 41 include sensing tubes 38 and40, respectively, which extend through the entire length of the heatexchange tube 72, internally thereof. The sensing fluid in the sensingtubes 38 and 40 is subject to expansion, contraction and vaporization inresponse to the temperatures existing along the heat exchange tube toprovide a signal for influencing boiler operation.

Still another embodiment of the invention is illustrated by FIGS. 4, 5,6A and 6B. A heat exchange means 85 includes a pair of headers 86 and 88which support therebetween a plurality of heat exchange tubes 90.Associated with the heat exchange means 85 is a control means 92. Thecontrol means 92 is characterized by sensing tubes 94 which extendsingly along the heat exchange tubes 90 rather than in pairs. Thecontrol means having a single sensing tube tends to be characterized bytube length limitations not experienced with the dual sensing tubecontrol means. As explained above in reference to FIGS. 1 and 2, if thesingle tube length is excessively long, the thermal expansion andcontraction of sensing fluid in the liquid state will be sufficientlylarge to create difficulty in distinguishing sensing tube expansioncaused by thermal expansion of the sensing fluid from sensing tubeexpansion caused by vaporization of the sensing fluid at a hot spotalong some segment of the heat exchange tube. If the ability todistinguish between these two signals is lost, the ability to detect hotspots is lost. However, for reasons including reasons of economy, it maybe advantageous to use the single sensing tube type of control mechanismin some applications.

The control means 92 will be described in connection with the systememploying three separate control devices, 93, 95 and 97. It should, ofcourse, be understood that any number of control devices could be used.The control device 93 includes the short sensing tube 94 which extendsalong the exterior of a pair of heat exchange tubes 90 and through theheader 88 to an expansible chamber, or bellows, 100. Extending from thebellows 100 is a plunger 106. Referring to FIGS. 6A and 6B, it will beseen that the plunger 106 is connected to a rocker arm 112 which isbiased by a compression spring 114 and pivoted at 116. The rocker armcooperates with a guide 118 which operates a microswitch 120 to controlthe burner for the heat exchange means, the burner for the apparatus ofFIG. 4 not being shown. A spring 122 is interposed between the bellows100 and the casing 124 to determine the pressure of the sensing fluid126 within the control device 93 and thereby the temperature at whichthe sensing fluid will vaporize, the vaporization temperature being themaximum working fluid temperature. The control devices 95 and 97 areeach contructed in exactly the same fashion as the control device 93.They include, respectively, short sensing tubes 96 and 98, bellows 102and 104, plungers 108 and 110, rocker arms 128 and 132 having pivotalconnections 130 and 134, and springs 136 and 138 interposed betweenbellows 102 and 104 and the casing 124. Each of the rocker arms 112, 128and 132 cooperate with the same guide 118 which enables them to operatethe single microswitch 120. The springs 112, 136 and 138 establishidentical sensing fluid pressure in each of the control devices 93, 95and 97.

When the apparatus of FIGS. 4 through 6 is in operation, working fluidpasses from the header 86 through the heat exchange tubes where it isvaporized and then into the header 88. From the header 88, the workingfluid vapor passes to other components of the system as will hereafterbe described. The products of combustion or other medium from which heatis to be transferred to the working fluid passes around the heatexchange tubes 90, through the spaces between them. The sensing fluidwithin the sensing tubes 94, 96 and 98 is responsive to the overallaverage temperature of the heat exchange tubes with which they areassociated. Expansion of the sensing fluids within the various controldevices 93, and 97 will all be relatively small and substantially equalwhen there is substantially uniform temperature within the heat exchangemeans 85. The system is constructed so that there is not enoughpotential thermal expansion of the sensing fluid to cause sufficientmovement of the rocker arms and to actuate the microswitch 120. Thesmall movement of the guide 118 which does take place is accomodated bythe space 140 which permits the guide to move up and down a littlewithout actuating the microswitch. However, if at least one linearsegment of the heat exchange tube 90 reaches the predetermined maximumtemperature for the working fluid within the heat exchange tubes 90,this relatively high temperature will cause vaporization of the sensingfluid within the adjacent segment of one of the sensing tubes. Thevaporization of the sensing fluid in even a small segment of a sensingtube will produce enough expansion in the fluid volume to operate themicroswitch. For example, if a hot spot develops along a heat exchangetube associated with sensing tube 94, the sensing fluid within thesensing tube 94 adjacent the hot spot will evaporate and significantlyincrease the volume of the sensing fluid within the sensing device 93.The bellows will expand and advance the plunger 106. The plunger 106will cause the rocker arm 112 to pivot about the support 116 and depressthe guide 118 by a sufficient amount to close.

the space 140 and operate the microswitch 120. The microswitch thensends a signal to the system for influencing the operation of theburner, not shown, associated with the heat exchange means 85. Since therocker arms associated with the various control devices all operate upona single microswitch, a hot spot occurring adjacent any one of thesensing tubes will causes the microswitch 120 to be actuated. Individualmicroswitches may be associated with each rocker arm so that the generallocation of the hot spot can be determined in accordance with which themicroswitch is actuated.

FIG. 7 illustrates schematically a Rankine cycle system incorporatingthis invention. The system includes the burner 36, boiler 12, andcontrol means 14. The working fluid which is evaporated in the boiler 12and passes to an expander 142 in which it expands to drive the shaft144. From the expander 142, the vaporized working fluid passes through aregenerator 146 where some of the remaining heat energy is extractedtherefrom. The vapor then passes through a condenser 148, is thereliquified, and a pump 1S0 drives the liquified working fluid from thecondenser 148 back through the regenerator 146. The liquified workingfluid is heated in the regenerator and then drive from the regeneratorback to the boiler 12 where it is vaporized and the cycle is repeated.

Referring to FIG. 2 with FIG. 7, when the system is operating, thecontrol means 14 monitors the temperature of the boiler as describedabove. Signals from the control means 14 are fed to the control logic152. The

control logic then produces a signal for either the burner cut-off means166 or the burner cut-down means 162.

When there is local overheating at even one small segment of the heatexchange tube in the boiler 12, the signal produced from the microswitch46 is directed through the control logic 152 to the burner cut-off means166. The cut-off means 166 commands the fuelair control means 164 tocompletely terminate the fuel and air supply to the burner 36. In thismanner, the system is shut down quickly so that permanent damage isavoided.

In embodiments which employ means responsive to the thermal expansionand contraction of the sensing fluid in its liquid state, the controllogic 152 provides a signal for operation of the burner cut-down. means162. The signal produced by the microswitch 59 is ultimately fed to theburner cut-down means 162 which reduces the fuel-air volume fed to theburner 36 and thereby reduces the overall temperature of the boiler 12.This may serve the usual function of a governor or it may sharply reducethe power output of the system while continuing to provide enough powerfor low level operation.

The present invention has been described with reference to variouspreferred embodiments. It should be understood, however, thatmodifications may be made by those skilled in the art without departingfrom the scope of this invention.

I claim:

1. A vapor engine boiler comprising:

a. elongated heat exchange tube means for conducting a working fluidalong a path in thermal communication with a heat source means;

b. first means extending along said heat exchange tube means andresponsive both to the average temperature change in said heat exchangetube means below a predetermined temperature and to the attainment ofsaid predetermined temperature in any segment of said heat exchange tubemeans;

c. second means extending along said heat exchange tube means andresponsive to the average temperature change in said heat exchange tubemeans; and

d. means responsive to said first and second means for producing asignal capable of influencing boiler operation when said predeterminedtemperature is attained at any segment of said heat exchange tube means.

2. A vapor engine boiler according to claim 1 wherein said first andsecond means each comprise a sealed sensing tube means filled withsensing fluid means, sensing fluid means in said first means vaporizingat said predetermined temperature and sensing fluid means in said secondmeans vaporizing at a substantially higher temperature than saidpredetermined temperature.

3. A vapor engine boiler according to claim 2 further comprising meansresponsive to said first and second means for respectively producing onesignal in response to the attainment of said predetermined temperaturein any segment of said heat exchange tube means and another signalproportional to the average temperature change in said heat exchangetube means.

4. A vapor engine boiler comprising:

a. heat source means;

b. elongated heat exchange tube means for conducting working fluid alonga path in thermal communication with said heat source means;

c. sealed sensing tube means extending along substantially the entirelenght of said heat exchange tube means in thermal communicationtherewith, said sensing tube means having a total crosssectional areawhich is small relative to the crosssectional area of said heat exchangetube means;

d. sensing fluid means filling said sensing tube means,

said sensing fluid means vaporizing at a temperature corresponding to apredetermined maximum temperature for said working fluid, whereby, asthe temperature of said working fluid reaches said predetermined maximumalong any segment thereof, sensing fluid means within the adjacentsegment of said sensing tube vaporizes to cause abrupt volumetricexpansion of said sensing fluid means; and

e. means responsive to abrupt expansion of said sensing fluid means forinfluencing the operation of said heat source means in response to theoccurance of said predetermined maximum temperature at any segmentalportion of said heat exchange tube means.

5. A vapor engine boiler according to claim 4 wherein said sensing fluidmeans extends along and engages said heat exchange tube means.

6. A vapor engine boiler according to claim 5 wherein said sensing tubemeans include expansion chamber means and said responsive means respondsto expansion and contraction of said expansible chamber means.

7. A vapor engine boiler comprising:

a. heat source means;

b. elongated heat exchange tube means for conducting working fluid alonga path in thermal communication with said heat source means;

c. a pair of hermetically sealed sensing tubes extending along said heatexchange tube means in thermal communication therewith, said sealedtubes having a total cross-sectional area which is small relative to thecross-sectional area of said heat exchange tube means;

d. sensing fluid means filling both said sealed tubes, said sensingfluid means being thermally expansible as a function of working fluidtemperature;

e. first expansion chamber means communicating with a first of saidsealed tubes;

f. first means biasing said first expansible chamber means to acompressed condition for applying to the sensing fluid means therein afirst pressure level, said biasing means causing said sensing fluidmeans in said first sealed tube to vaporize at a temperaturecorresponding to a maximum temperature for said working fluid whereby,as the temperature of said working fluid reaches said maximumtemperature along any segment of its length, said sensing fluid meanswithin the adjacent segmental length of said first sensing tubevaporizes to cause volumetric expansion of said first expansion chambermeans for influencing operation of said heat source means in response totemperature conditions at relatively short segments of said heatexchange tube means;

g. second expansible chamber means communicating with a second of saidsealed tubes; and

h. second means biasing said second expansible chamber means to acompressed condition for applying to the sensing fluid therein a secondpressure level, said second pressure level being sufficiently high tocause said sensing fluid means in said second sealed tube to vaporize ata temperature above said maximum temperature for said working fluid,whereby two signals are produced, a first of said signals beingproportional to temperature change below said maximum temperature andalso responsive to the attainment of said maximum temperature along anysegment of said heat exchange tube, the second of said signals beingproportional to temperature change both below and above said maximumtemperature and independent of said maximum temperature; and

i. means responsive to said first and second signals for influencing theoperation of said heat source means as a function of the occurance ofsaid maximumtemperature along any segment of said first sealed tube.

8. A vapor engine boiler according to claim 7 wherein said responsivemeans responds to both said first signal and said second signal forinfluencing said heat source means as a function of the occurrence ofsaid maximum temperature along any segment of said heat exchange tubemeans.

9. A vapor engine boiler comprising:

a. heat source means;

b. elongated heat exchange tube means for conducting working fluid alonga path in thermal communication with said heat source means;

c. sealed sensing tube means extending along said heat exchange tubemeans in thermal communication therewith, said sensing tube means havinga total cross-sectional area which is small relative to thecross-sectional area of said heat exchange tube means;

(1. sensing fluid means filling said sensing tube means, said sensingfluid means being thermally expansible as a function of working fluidtemperature;

e. means for applying pressure to said sensing fluid means in saidsensing tube means for establishing a predetermined vaporizationtemperature of said sensing fluid means whereby, as the temperature ofsaid working fluid within any segment of said heat exchange tube meansreaches a temperature level substantially equalling such predeterminedvaporization temperature, said sensing fluid means within the adjacentsegmental length of said sensing tube means vaporizes; and

f. means responsive to vaporization of said sensing fluid means forinfluencing the operation of said heat source means. 10. A vapor engineboiler according to claim 9 wherein said responsive means is alsoresponsive to thermal expansion and contraction of said sensing fluidmeans for influencing said heat source in response thereto.

11. A vapor engine boiler comprising:

a. heat source means; b. thermally sensitive working fluid for saidvapor engine;

c. elongated heat exchange tube means for conducting said working fluidalong a path in thermal communication with said heat source means;

(1. sealed sensing tube means extending along a substantial length ofsaid heat exchange tube means in thermal communication therewith, saidsensing tube means having a total cross-sectional area which is smallrelative to the cross-sectional area of said heat exchange tube means;

e. sensing fluid means filling said sensing tube means,

said sensing fluid means being thermally expansible as a function ofworking fluid temperature;

f. means for maintaining the pressure internal of said g. meansresponsive to the expansion of said sensing fluid means attending suchvaporization thereof for reducing the heat output of said heat sourcemeans.

1. A vapor engine boiler comprising: a. elongated heat exchange tubemeans for conducting a working fluid along a path in thermalcommunication with a heat source means; b. first means extending alongsaid heat exchange tube means and responsive both to the averagetemperature change in said heat exchange tube means below apredetermined temperature and to the attainment of Said predeterminedtemperature in any segment of said heat exchange tube means; c. secondmeans extending along said heat exchange tube means and responsive tothe average temperature change in said heat exchange tube means; and d.means responsive to said first and second means for producing a signalcapable of influencing boiler operation when said predeterminedtemperature is attained at any segment of said heat exchange tube means.2. A vapor engine boiler according to claim 1 wherein said first andsecond means each comprise a sealed sensing tube means filled withsensing fluid means, sensing fluid means in said first means vaporizingat said predetermined temperature and sensing fluid means in said secondmeans vaporizing at a substantially higher temperature than saidpredetermined temperature.
 3. A vapor engine boiler according to claim 2further comprising means responsive to said first and second means forrespectively producing one signal in response to the attainment of saidpredetermined temperature in any segment of said heat exchange tubemeans and another signal proportional to the average temperature changein said heat exchange tube means.
 4. A vapor engine boiler comprising:a. heat source means; b. elongated heat exchange tube means forconducting working fluid along a path in thermal communication with saidheat source means; c. sealed sensing tube means extending alongsubstantially the entire lenght of said heat exchange tube means inthermal communication therewith, said sensing tube means having a totalcross-sectional area which is small relative to the cross-sectional areaof said heat exchange tube means; d. sensing fluid means filling saidsensing tube means, said sensing fluid means vaporizing at a temperaturecorresponding to a predetermined maximum temperature for said workingfluid, whereby, as the temperature of said working fluid reaches saidpredetermined maximum along any segment thereof, sensing fluid meanswithin the adjacent segment of said sensing tube vaporizes to causeabrupt volumetric expansion of said sensing fluid means; and e. meansresponsive to abrupt expansion of said sensing fluid means forinfluencing the operation of said heat source means in response to theoccurance of said predetermined maximum temperature at any segmentalportion of said heat exchange tube means.
 5. A vapor engine boileraccording to claim 4 wherein said sensing fluid means extends along andengages said heat exchange tube means.
 6. A vapor engine boileraccording to claim 5 wherein said sensing tube means include expansionchamber means and said responsive means responds to expansion andcontraction of said expansible chamber means.
 7. A vapor engine boilercomprising: a. heat source means; b. elongated heat exchange tube meansfor conducting working fluid along a path in thermal communication withsaid heat source means; c. a pair of hermetically sealed sensing tubesextending along said heat exchange tube means in thermal communicationtherewith, said sealed tubes having a total cross-sectional area whichis small relative to the cross-sectional area of said heat exchange tubemeans; d. sensing fluid means filling both said sealed tubes, saidsensing fluid means being thermally expansible as a function of workingfluid temperature; e. first expansion chamber means communicating with afirst of said sealed tubes; f. first means biasing said first expansiblechamber means to a compressed condition for applying to the sensingfluid means therein a first pressure level, said biasing means causingsaid sensing fluid means in said first sealed tube to vaporize at atemperature corresponding to a maximum temperature for said workingfluid whereby, as the temperature of said working fluid reaches saidmaximum temperature along any segment of its length, said sensing fluidmeans within the adjacent segmental length of said first sensing tubevaporizes to cause volumetric expansion oF said first expansion chambermeans for influencing operation of said heat source means in response totemperature conditions at relatively short segments of said heatexchange tube means; g. second expansible chamber means communicatingwith a second of said sealed tubes; and h. second means biasing saidsecond expansible chamber means to a compressed condition for applyingto the sensing fluid therein a second pressure level, said secondpressure level being sufficiently high to cause said sensing fluid meansin said second sealed tube to vaporize at a temperature above saidmaximum temperature for said working fluid, whereby two signals areproduced, a first of said signals being proportional to temperaturechange below said maximum temperature and also responsive to theattainment of said maximum temperature along any segment of said heatexchange tube, the second of said signals being proportional totemperature change both below and above said maximum temperature andindependent of said maximum temperature; and i. means responsive to saidfirst and second signals for influencing the operation of said heatsource means as a function of the occurance of said maximum temperaturealong any segment of said first sealed tube.
 8. A vapor engine boileraccording to claim 7 wherein said responsive means responds to both saidfirst signal and said second signal for influencing said heat sourcemeans as a function of the occurrence of said maximum temperature alongany segment of said heat exchange tube means.
 9. A vapor engine boilercomprising: a. heat source means; b. elongated heat exchange tube meansfor conducting working fluid along a path in thermal communication withsaid heat source means; c. sealed sensing tube means extending alongsaid heat exchange tube means in thermal communication therewith, saidsensing tube means having a total cross-sectional area which is smallrelative to the cross-sectional area of said heat exchange tube means;d. sensing fluid means filling said sensing tube means, said sensingfluid means being thermally expansible as a function of working fluidtemperature; e. means for applying pressure to said sensing fluid meansin said sensing tube means for establishing a predetermined vaporizationtemperature of said sensing fluid means whereby, as the temperature ofsaid working fluid within any segment of said heat exchange tube meansreaches a temperature level substantially equalling such predeterminedvaporization temperature, said sensing fluid means within the adjacentsegmental length of said sensing tube means vaporizes; and f. meansresponsive to vaporization of said sensing fluid means for influencingthe operation of said heat source means.
 10. A vapor engine boileraccording to claim 9 wherein said responsive means is also responsive tothermal expansion and contraction of said sensing fluid means forinfluencing said heat source in response thereto.
 11. A vapor engineboiler comprising: a. heat source means; b. thermally sensitive workingfluid for said vapor engine; c. elongated heat exchange tube means forconducting said working fluid along a path in thermal communication withsaid heat source means; d. sealed sensing tube means extending along asubstantial length of said heat exchange tube means in thermalcommunication therewith, said sensing tube means having a totalcross-sectional area which is small relative to the cross-sectional areaof said heat exchange tube means; e. sensing fluid means filling saidsensing tube means, said sensing fluid means being thermally expansibleas a function of working fluid temperature; f. means for maintaining thepressure internal of said sensing tube means at a value which willresult in vaporization of said sensing fluid means at a predeterminedtemperature substantially equalling the maximum temperature to whichsaid working fluid can be heated without deterioration, whereby as thetemperature of said working fluid within any segment of said heatexchange tube means reaches said predetermined temperature said sensingfluid means within the adjacent segment of said sensing tube meansvaporizes; and g. means responsive to the expansion of said sensingfluid means attending such vaporization thereof for reducing the heatoutput of said heat source means.